1. Technical Field
This disclosure relates to a device and method for detecting the wiring state in a network.
2. Description of the Related Art
Onboard networks for entertainment systems used on aircraft are sometimes connected with a twisted pair cable. A twisted pair cable is called 10BASE-T or 100BASE-TX (hereinafter these two will be collectively referred to as 10/100BASE-TX), which have been standardized as a LAN standard by IEEE (Institute of Electrical and Electronics Engineers (US)) 802.3 as a transmission medium for connecting devices.
There are two kinds of 10/100BASE-TX cable: a straight cable and a crossover cable (see Japanese Laid-Open Patent Application 2001-291564, for example). However, the quality and reliability of communication device must be improved by eliminating as many uncertain elements as possible in wiring. In particular, in Ethernet® communication between devices, the devices are sometimes connected by straight or crossover cable by fixing the transmission and reception directions and disabling the automatic switching between MDI (medium dependent interface) and MDI-X (medium dependent interface crossover) and determining ahead of time the pin layout for transmission and reception in the devices. Also, depending on the communication method, two lines may be readied for a transmitter and a receiver since data communication performed in a single frequency band is limited to one direction, or the orientation of a single line may be periodically inverted. The former is called full-duplex communication (hereinafter referred to as full-duplex), while the latter is called half-duplex communication (hereinafter referred to as half-duplex).
Automatically determining whether the communication method will be full-duplex or half-duplex communication is the norm in consumer applications, but the method is sometimes predetermined in network wiring used in aircraft. Aircraft network wiring is rarely changed after the system has been installed, except for during major modifications such as major remodeling of the aircraft interior, so the signal layout between devices is also rarely changed.
In general, devices that are installed in an aircraft are subjected to different conditions from those of consumer devices, such as vibrations and temperature changes, electrical and magnetic disturbances during flight, and the need for materials to be flame retardant. Thus, the wiring material (harness) of the network is sometimes a dedicated harness that uses special cables that are resistant in a variety of situations, rather than the Ethernet® cables that are commonly used.
Aircraft come in many different combinations of seat configuration and type of fuselage, so these dedicated harnesses cannot be mass produced, and incorrect wiring or broken connections often occur due to human error. When a device is installed in an aircraft, a network is wired, and then the power is switched on for testing, problems can occur in which network communication does not work.
If this happens, whether the reason behind the problem is malfunction of the device or incorrect wiring is not immediately apparent, so both the device and the harness have to be checked, which takes a great deal of time. With general-purpose consumer devices and the like, a method has been adopted in which communication is established by utilizing an automatic MDI/MDI-X switching function when the straight/crossover connection of Ethernet® wiring is reversed between devices due to incorrect wiring.
However, as mentioned above, with network wiring used in an aircraft, there are many required specifications such as disabling auto-negotiation or the MDI/MDI-X switching of devices, and in such cases communication cannot be established. This makes it impossible to determine whether the cause is a device malfunction or incorrect wiring. Furthermore, since aircraft-use network wiring requires the production of a dedicated harness as mentioned above, other causes of disconnection frequently occur besides incorrect straight or crossover wiring, and in this case detection is impossible by the above method.